XIV PEOCEEDINGS OF THE 



It was then known that, besides the nucleus which occupied a con- 

 spicuous position in the protoplasmic mass, there existed in many 

 Infusoria another differentiated body, similar to the nucleus, but 

 smaller, and either in close contact with it, or separated from it by 

 a greater or less interval. To this body the ill-chosen name of 

 "nucleolus" had been given. Now Balbiani's observations led him 

 to believe that, under the influence of conjugation, this so-called 

 nucleolus underwent a change, and developed in its interior a mul- 

 titude of exceedingly minute filaments or rod-like bodies, to which 

 he attributed the significance of spermatozoa ; while at the same time 

 the nucleus became divided into globular masses, which Balbiani 

 regarded as eggs, and in which he believed he could recognize a 

 germinal vesicle and germinal spot. AVe should thus, according to 

 this interpretation, have in the Infusoria the two essential elements 

 of sexual differentiation, the spermatozoon and the egg. 



Stein, though differing from Balbiani in certain details, accepts, 

 in its general facts, the sexual theory, and maintains the spermatic 

 nature of the rod-like corpuscles to which the nucleolus appears to 

 give rise. 



But however real may be the phenomena described by Balbiani 

 and by Stein, the correctness of assigning to them a sexual signifi- 

 cance may be called in question ; and it is certain that subsequent 

 observation has not tended to confirm the hypothesis that we have 

 in the Infusoria true eggs fecundated by true spermatozoa. 



Claparede and Lachmann, two able and indefatigable observers fresh 

 from the school of the great anatomist Johannes Miiller, now entered 

 the field, and their joint labours have given us a most valuable work 

 on the Infusoria*. In this an entirely new view of the morphology 

 of the Infusoria has been introduced. Receding widely from the 

 unicellular theory of Siebold, they approximate towards the views of 

 Ehrenberg in assigning to the Infusoria a comparatively complex 

 structure ; but instead ^of adopting the polygastric theory of the 

 Prussian microscopist, they attribute to the Infusoria a single well- 

 defined gastric cavity, occupying the whole of the space limited ex- 

 ternally by the outer firm boundary-walls of the softer protoplasmic 

 mass ; while this mass is regarded by them as nothing more than a 

 sort of chyme by which the gastric cavity is filled. According to 

 this view, the nearest relations of the Infusoria would be found 

 among the Zoophytes, and their proper systematic seat would be in 

 the primary group of the Ccelenterata. 



* Claparede et Lachmann, 'Etudes siir les Infusoires et les Ehizopodes.' 

 Geneve, 1858-1861. 



